The pre-sent invention relates generally to an apparatus and method for noninvasive monitoring of one or more cardiac performance parameters, and more particularly to a method and an apparatus determining mean left atrial pressure.
The diagnosis and care of patients with cardiovascular disease critically depends on information about the pumping ability of the heart. For example, the priming pressure of the left ventricle of the heart, typically obtained by measurement of left atrial pressure, indicates, when abnormal, a mismatch between volume capacity of the vascular system and the circulatory blood volume.
Since the early 1970""s, the flow-directed pulmonary artery balloon catheter (a.k.a. the Swan-Ganz catheter) has been the standard for bedside hemodynamic monitoring. It yields cardiac output by thermodilution as well as an estimate of mean left atrial pressure. However, under certain conditions, the pressure readings may not faithfully reflect left atrial pressure (R. RAPER et al, xe2x80x9cMisled by the Wedgexe2x80x9d, Chest, March 1986, pp. 427-434). This invasive technique is personnel intensive and costly since the catheter must be inserted and used in a critical care area or operating room, and it has been associated with infection, arrhythmias, and death (E. ROBIN et al, xe2x80x9cThe Cult of the Swan-Ganz Catheterxe2x80x9d, Annals of Internal Medicine, September 1985, vol. 103, pp. 445-449). Its use is further limited since it only provides non-automated intermittent measurements, and the catheter should, for safety reasons, only be left in the patient for a few days.
My U.S. Pat. Nos. 5,048,532; 5,181,517; 5,263,4.85; 5,398,692; 5,551,439; 5,570,671; 5,697,375; and 5,921,935, the disclosures of all of which patents are incorporated herein by reference, disclose noninvasive methods and apparatus which includes a catheter containing an inflatable balloon insertable into the esophagus for placement adjacent the left atrium, and associated equipment for making determinations of-mean left atrial pressure. When the inflated balloon is adjacent the left atrium and receiving pressure waves therefrom, the balloon pressure oscillates. As the balloon pressure is gradually increased, the balloon oscillations reach a peak or point of maximum oscillatory amplitude. As discussed in my prior patents, this peak is believed to occur when the balloon pressure is equal to the mean left atrial pressure. Thus, a determination of mean left atrial pressure may be made by noting the balloon pressure at the oscillatory peak.
As discussed in the parent patent to this application, the mean left atrial pressure as determined above may be used in conjunction with the effects of aortic pressure on an inflated balloon to noninvasively and more comprehensively provide cardiac performance information.
While the above technique for determining mean left atrial pressure has been shown experimentally to be accurate, there have nevertheless been instances where the mean left atrial pressure as determined by the above technique has tended to be over estimated, i.e., showing a greater mean left atrial pressure than the actual mean left atrial pressure.
It is accordingly an object of this invention to noninvasively and more precisely determine mean left atrial pressure.
In order to noninvasively and more precisely determine mean left atrial pressure, in accordance with the present invention, the wave form of the balloon pressure oscillations is subjected to fast Fourier transform analysis to apply a catheter transfer function to each of the component waves thereof to correct the amplitudes thereof, and a corrected wave form reconstructed from the corrected component waves.
The above and other objects, features, and advantages of this invention will become apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings wherein the same reference numerals denote the same or similar parts or items throughout the several views and in which a preferred embodiment of this invention is illustrated.